I think his point was that the Apple/Mac ethos foster high quality design and attention to detail, which is applied when developers build apps for the Mac.
To be fair, so does elementaryOS. They really try to encourage developers to adopt their HIG.[1]
So much so that most developers using or targeting elementaryOS integrate their design really well.[2] For those that don't but still use GTK3, they also integrate quite well out of the box.
